Method and arrangement in a hybrid vehicle for maximizing total torque output by minimizing differential torque capacities of the engine and generator

ABSTRACT

Method for potentiating the utilizable torque output capacity of a hybrid electric vehicle is disclosed. The method includes controlling operation of an engine of a hybrid electric vehicle using a generator, the engine and generator being interconnected through a planetary gear system, the generator having approximately equal torque output capacity as the engine based on connective gear ratio selection. An engine controller is utilized for managing the engine&#39;s operation thereby permitting the engine to be operated at a torque output level substantially equal to the maximum torque output of the generator without a significant margin of excess control capacity of the generator over the engine. An overpower condition is detected in which the torque output of the engine is surpassing the maximum torque output of the generator. The engine is controlled to a torque output that is less than the maximum torque output of the generator.

RELATED APPLICATION(S)

[0001] This patent application claims priority to U.S. ProvisionalApplication No. 60/245,090 filed Oct. 31, 2000 and entitled HYBRIDELECTRIC VEHICLE. Said application in its entirety is hereby expresslyincorporated by reference into the present application.

DESCRIPTION

[0002] 1. Industrial Applicability

[0003] The present invention finds applicability in the transportationindustries, and more specifically private and commercial vehicles. Ofparticular importance is the invention's incorporation into hybridelectric vehicles.

[0004] 2. Background Art

[0005] Generally, a hybrid electric vehicle combines electric propulsionwith traditional internal combustion engine propulsion to achieveenhanced fuel economy and/or lower exhaust emissions. Electricpropulsion has typically been generated through the use of batteries andelectric motors. Such an electric propulsion system provides thedesirable characteristics of high torque at low speeds, high efficiency,and the opportunity to regeneratively capture otherwise lost brakingenergy. Propulsion from an internal combustion engine provides highenergy density, and enjoys an existing infrastructure and lower costsdue to economies of scale. By combining the two propulsive systems witha proper control strategy, the result is a reduction in the use of eachdevice in its less efficient range. Furthermore, and as shown in FIG. 1regarding a parallel hybrid configuration, the combination of adownsized engine with an electric propulsion system into a minimalhybrid electric vehicle results in a better utilization of the engine,which improves fuel consumption. Furthermore, the electric motor andbattery can compensate for reduction in the engine size.

[0006] In typical configurations, the combination of the two types ofpropulsion systems internal combustion and electric) is usuallycharacterized as either series or parallel hybrid systems. In a pureseries hybrid propulsion system, only the electric motor(s) are indirect connection with the drive train and the engine is used togenerate electricity which is fed to the electric motor(s). Theadvantage of this type of system is that the engine can be controlledindependently of driving conditions and can therefore be consistentlyrun in its optimum efficiency and low emission ranges. A keydisadvantage to the series arrangement is the loss in energy experiencedbecause of the inefficiencies associated with full conversion of theengine output to electricity.

[0007] In a pure parallel hybrid propulsion system, both the engine andthe electric motor(s) are directly connected to the drive train andeither one may independently drive the vehicle. Because there is adirect mechanical connection between the engine and the drive train in aparallel hybrid propulsion system, less energy is lost throughconversion to electricity compared to a series hybrid propulsion system.The operating point for the engine, however, can not always be chosenwith full freedom.

[0008] The two hybrid propulsion systems can be combined into either aswitching hybrid propulsion system or a power-split hybrid propulsionsystem. A switching hybrid propulsion system typically includes anengine, a generator, a motor and a clutch. The engine is typicallyconnected to the generator. The generator is connected through a clutchto the drive train. The motor is connected to the drive train betweenthe clutch and the drive train. The clutch can be operated to allowseries or parallel hybrid propulsion.

[0009] A power-split hybrid system, as is exemplarily employed withrespect to the present invention, includes an engine, a generator and amotor. The engine output is “split” by a planetary gear set into aseries path from the engine to the generator and a parallel path fromthe engine directly to the power train. In a power-split hybrid system,the engine speed can be controlled by varying the power split to thegenerator by way of the series path, while maintaining the mechanicalconnection between the engine and drive train through the parallel path.The motor augments the engine on the parallel path in a similar manneras a traction motor in a pure parallel hybrid propulsion system, andprovides an opportunity to use energy directly through the series path,thereby reducing the losses associated with converting the electricalenergy into, and out of chemical energy at the battery.

[0010] In a typical power-split hybrid system, the generator is usuallyconnected to the sun gear of the planetary gear set. The engine isconnected to the planetary carrier and the output gears (usuallyincluding an output shaft and gears for interconnection with the motorand the wheel-powering, final drive train) are connected to the ringgear. In such a configuration, the power-split hybrid system cangenerally be operated in four different modes; one electric mode andthree hybrid modes.

[0011] In the electric mode, the power-split hybrid system propels thevehicle utilizing only stored electrical energy and the engine is turnedoff. The tractive torque is supplied from the motor, the generator, or acombination of both. This is the preferred mode when the desired poweris low enough that it can be produced more efficiently by the electricalsystem than by the engine and when the battery is sufficiently charged.This is also a preferred mode for reverse driving because the enginecannot provide reverse torque to the power train in this configuration.

[0012] In the parallel hybrid mode, the engine is operating and thegenerator is locked. By doing this, a fixed relationship between thespeed of the engine and the vehicle speed is established. The motoroperates as either a motor to provide tractive torque to supplement theengine's power, or can be operated to produce electricity as agenerator. This is a preferred mode whenever the required power demandrequires engine operation and the required driving power isapproximately equal to an optimized operating condition of the engine.This mode is especially suitable for cruising speeds exclusivelymaintainable by the small internal combustion engine fitted to thehybrid electric vehicle.

[0013] In a positive split hybrid mode, the engine is on and its poweris split between a direct mechanical path to the drive train and anelectrical path through the generator. The engine speed in this mode istypically higher than the engine speed in the parallel mode, thusderiving higher engine power. The electrical energy produced by thegenerator can flow to the battery for storage or to the motor forimmediate utilization. In the positive split mode, the motor can beoperated as either a motor to provide tractive torque to supplement theengine's power or to produce electricity supplementally with thegenerator. This is the preferred mode whenever high engine power isrequired for tractive powering of the vehicle, such as when highmagnitude acceleration is called for, as in passing or uphill ascents.This is also a preferred mode when the battery is charging.

[0014] In a negative split hybrid mode, the engine is in operation andthe generator is being used as a motor against the engine to reduce itsspeed. Consequently, engine speed, and therefore engine power, are lowerthan in parallel mode. If needed, the motor can also be operated toprovide tractive torque to the drive train or to generate electricitytherefrom. This mode is typically never preferred due to increasedlosses at the generator and planetary gear system, but will be utilizedwhen engine power is required to be decreased below that which wouldotherwise be produced in parallel mode. This situation will typically bebrought about because the battery is in a well charged condition and/orthere is low tractive power demand. In this regard, whether operating asa generator or motor, the toque output of the generator is always of thesame sense (+/−); that is, having a torque that is always directionallyopposed to that of the engine. The sign of the speed of the generator,however, alternates between negative and positive values depending uponthe direction of rotation of its rotary shaft, which corresponds withgenerator vs. motor modes. Because power is dependent upon the sense ofthe speed (torque remains of the same sense), the power will beconsidered to be positive when the generator is acting as a generatorand negative when the generator is acting as a motor.

[0015] When desiring to slow the speed of the engine, the current beingsupplied to the generator is changed causing the speed of the generatorto slow. Through the planetary gear set, this in turn slows the engine.This effect is accomplished because the resistive force acting againstthe torque of the generator is less at the engine than at the driveshaft which is connected to the wheels and is being influenced by theentire mass of the vehicle. It should be appreciated that the change inspeed of the generator is not equal, but instead proportional to that ofthe engine because of gearing ratios involved within the connectiontherebetween.

[0016] In electric and hybrid electric vehicles, large capacityelectricity storage device(s), usually in the form of battery packs, arerequired. By conventional design, these batteries include a plurality ofcylindrical battery cells that are collectively utilized to obtainsufficient performance and range in the vehicle. Typically, batteriesare positioned within the vehicle in a compartment configured to protectagainst damage and to prevent the cells, and mostly their acidiccontents, from causing injury or damage, especially in the event of acrash. When stored in these typically confined compartment(s), heatbuildup generated from use and/or charging affects the endurance of thebatteries, and in some circumstances can destroy individual batterycells. Traditional cooling of the batteries and the battery compartmentrequires increasing the volume of the compartment for air cooling and/orrunning cooling hoses to external radiators.

[0017] Typically, to achieve a smooth engine start in a hybrid electricvehicle in which the engine is mechanically interconnected with thedrive wheels, the start of engine fuel injection and ignition are madeat revolutionary speeds above any mechanical resonance speeds of thedrive train. Additionally, at full take-off acceleration, any delay inthe engine's production of power typically decreases engine performance.Still further, to achieve smooth driving characteristics and obtain lowfuel consumption, the engine torque and speed change rates must belimited. At full take-off, this usually results in an increased timeperiod for the engine to reach maximum power, and all of theseconditions deteriorate acceleration performance of the vehicle.

[0018] As can be appreciated, the engine is not always running duringvehicle operation. If the engine is stopped for a sufficiently longperiod during the operation of the vehicle, the exhaust system catalystmay cool down too much, and to such a degree that a temporary, butsignificant increase in exhaust emissions occur upon restart and untilthe catalyst once again warms to its effective temperature.

[0019] In another aspect, the battery state-of-charge (SOC) in a hybridelectric vehicle is typically controlled using SOC feedback control.When applying SOC feedback control, however, and when the vehicle isoperating in a low velocity region, the SOC feedback control tends togrow unstable as velocity increases. Instability also occurs when thevehicle is operating at high velocity and the velocity of the vehiclethen decreases. The same instability or weakness can still occur evenwhen using “feed-forward” type estimating of required tractive force;the same being a typical complement to SOC feedback control. This isparticularly true at low vehicle velocities with velocity increases andat high vehicle velocities with velocity decreases. Even when properlydesigned, the SOC feedback control can also be weak at full take-off.

[0020] In a typical power-split hybrid electric propulsion arrangement,the control strategy advantageously involves operating the engine alongoptimum efficiency torque vs. speed curves. A trade-off exists betweentraction force performance and fuel economy which, for optimization,typically requires selection of a particular gear ratio between theengine and the wheels that causes the engine to deliver more power thanis needed for vehicle propulsion. This generally occurs at cruising inparallel mode, or near constant vehicle velocity conditions. Operationunder these conditions can, sometimes, cause the battery and chargingsystem to reject energy being presented thereto from the engine. Thisproblem is generally solved by decreasing or limiting the engine outputpower by entering negative split mode which entails using the generatoras a motor to control the engine to a decreased speed. Such controlallows the engine to follow an optimum curve at reduced engine outputpower.

[0021] Use of the generator as a motor gives rise to a power circulationin the power-train which leads to undesirable energy losses at thegenerator, motor, inverters and/or planetary gear set. These energylosses may be manifest as heat generation which indicates that mostefficient use is not being made of the installed drive train.

[0022] In a power-split hybrid propulsion system having planetary gearset(s) and utilizing a generator lock-up device, a harshness in rideoccurs when the generator lock-up device is engaged or released. This isdue primarily to the difference in how engine torque is estimated whenthe vehicle is in different operating modes. Typically, when thegenerator is locked up, engine torque is estimated from the combustioncontrol process of the engine. When the generator is free, as in splitmode, however, engine torque is estimated from the generator torquecontrol process. The difference in values of these two estimatingtechniques gives rise to what usually amounts to a variation inoperating torque between the engine and generator when the lock-updevice is engaged or disengaged, thereby creating harshness in thevehicle's operation, usually manifest as abrupt changes or jerkiness inthe vehicle's ride.

[0023] As earlier indicated, the generator is typically used to controlthe engine in power-split hybrid mode. This is usually accomplished byemploying a generator having maximum torque capabilities substantiallygreater than the engine's maximum torque that is transmittable to theplanetary gear system. Failure to have such a control margin can resultin generator over-speed and possible damage to the propulsion system.Such a control margin means, however, that the engine and generator arenot fully exploited at full capacity acceleration.

[0024] Several deficiencies associated with the use of known hybridelectric vehicle designs and methods of operating the same have beendescribed hereinabove. Several inventive arrangements and methods foroperating hybrid electric vehicles are described hereinbelow thatminimize, or remedy these deficient aspects of known designs, and/orprovide benefits, in and of themselves, to the user. These new, improvedand otherwise potentiated solutions are described in greater detailhereinbelow with respect to several alternative embodiments of thepresent invention.

DISCLOSURE OF THE INVENTION

[0025] In a first aspect, an arrangement for a compact battery andcooling system therefore is disclosed. The arrangement includes aplurality of elongate battery cells, each battery cell having alongitudinal axis and a hexagonal cross-sectional shape in a planeoriented substantially perpendicular to the longitudinal axis. The cellsare parallelly oriented, each to the others, within a battery housing.Preferably, the cells are arranged in a honeycomb configuration withopposed faces of adjacent battery cells proximately located one to theother in face-to-face relationship. At least one substantiallyhexagonally shaped cooling channel is provided at an interior locationwithin the plurality of battery cells.

[0026] In a second aspect, a method for potentiating an engine's powercontribution to a hybrid electric vehicle's performance in a take-offoperating condition is disclosed. Normally, fuel injection to, andignition at the engine are only commenced when the engine is operatingat a speed exceeding the resonance speed of the drive train to reduceengine start harshness; such resonance speeds of the drive train beingdictated, at least in part, by transmission backlash, softness and thelike. During high driver acceleration demands, however, ignition and theinjection of fuel is desirably started as early as possible topotentiate output power and acceleration.

[0027] In a third aspect, a method for maintaining a catalyst of anemissions system in a hybrid electric vehicle in an operative conditionis disclosed. The method includes sensing that an engine of a hybridelectric vehicle has stopped operating. A time period is predicted afterwhich a catalyst of an emissions system associated with the engine willcool to a light-off temperature below which the catalyst becomesineffective. The predicting step is based on known qualities of thecatalyst and ambient conditions in which the vehicle is being operated.The engine is restarted when the predicted time period has expiredthereby maintaining the catalyst at temperatures in excess of thelight-off temperature.

[0028] In a fourth aspect, a method for minimizing driver perceptibledrive train disturbances during take-off in a hybrid electric vehiclewhen maximized power is often desired is disclosed. The method includessensing an actual state-of-charge (SOC) value of a battery in a hybridelectric vehicle and a traveling velocity of the vehicle during take-offoperation. The sensed actual SOC value is compared with a SOC referencevalue and computing a delta SOC value as a difference therebetween. Avelocity-based SOC calibration factor is looked up that corresponds tothe traveling velocity of the vehicle. A combination is utilized of thedelta SOC value and the SOC calibration factor as a SOC feedback enginespeed control instruction to an engine controller of the hybrid electricvehicle. A driver's desired vehicular acceleration is sensed based onaccelerator position. Maximum possible engine power generatable at thesensed vehicle speed is determined, as is a required power value fromthe power train of the vehicle to meet the driver's desired vehicularacceleration. The maximum possible engine power generatable at thesensed vehicle speed is compared with the required power value andcomputing a delta power train requirement value as a differencetherebetween. A velocity-based and accelerator position-based powercalibration factor is looked-up that corresponds to the travelingvelocity of the vehicle and the accelerator position. A combination ofthe delta power train requirement value and the power calibration factoris utilized as a power requirement feed-forward engine speed controlinstruction to an engine controller of the hybrid electric vehicle.

[0029] In a fifth aspect, a method for optimizing the operationalefficiency of a hybrid electric vehicle is disclosed. The methodcomprises operating an engine of a hybrid electric vehiclepreferentially on an optimized power curve of the engine for maximizingthe efficiency of the engine and sensing a state-of-charge (SOC)condition of a battery of the hybrid electric vehicle being at apreferential value indicative of no additional charging being desired.The running torque of the engine is reduced below the optimized torquecurve to a point that the power produced by the engine is substantiallyequal to the power demanded for driving the hybrid electric vehicle.

[0030] In a sixth aspect, a method for calibrating and synchronizingsensed operating torques of an engine and a generator in a planetarygear based hybrid electric vehicle is disclosed. The method includesproviding a sensor that detects the operational torque of an engine of ahybrid electric vehicle at the engine's interface with a planetary gearsystem of the hybrid electric vehicle. A sensor is provided that detectsthe operational torque of a generator of a hybrid electric vehicle atthe motor's interface with the planetary gear system of the hybridelectric vehicle. The planetary gear system of the hybrid electricvehicle is operated in a split mode so that the generator is directlylinked to the engine and a reading of the sensor that detects theoperational torque of the generator may be used to compute the operatingtorque of the engine. Paired values of sensed operational torques of theengine and the generator at like times are recorded. Each pair ofrecorded values are arithmetically processed and a calibrating value iscomputed therebetween. The sensing and recording of paired values isrepeated at the same sensed generator and engine speeds and torquesthereby enabling the calculation of computed average calibrating valuesat each of the particular sensed generator speeds suitable forsubsequent utilization in computing corresponding engine torques in thefuture. The engine and the generator are controlled utilizing theaverage calibrating value at future times of transition betweenpower-split mode and parallel mode of the planetary gear system so thatthe engine is substantially synchronized with the generator at the timeof direct linkage across the planetary gear arrangement thereby avoidingdriver detectible irregularities in the performance of the power trainof the hybrid electric vehicle.

[0031] In a seventh aspect, a method for potentiating the utilizabletorque output capacity of a hybrid electric vehicle is disclosed. Themethod includes controlling operation of an engine of a hybrid electricvehicle using a generator, the engine and generator being interconnectedthrough a planetary gear system, the generator having approximatelyequal torque output capacity as the engine based on connective gearratio selection. An engine controller is utilized for managing theengine's operation thereby permitting the engine to be operated at atorque output level substantially equal to the maximum torque output ofthe generator without a significant margin of excess control capacity ofthe generator over the engine. An overpower condition is detected inwhich the torque output of the engine is surpassing the maximum torqueoutput of the generator. The engine is controlled to a torque outputthat is less than the maximum torque output of the generator.

[0032] The general beneficial effects described above apply generally tothe exemplary descriptions and characterizations of the devices,mechanisms and methods disclosed herein. The specific structures andsteps through which these benefits are delivered will be described indetail hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In the following, the invention will be described in greaterdetail by way of examples and with reference to the attached drawings,in which:

[0034]FIG. 1 is a graphical comparison of torque generated by a parallelhybrid and systems that have either an engine or motor.

[0035]FIG. 2 is a perspective of a hybrid electric vehicle showingexemplarily system component locations on the vehicle.

[0036]FIG. 3 is a schematic depicting the architecture of a power-splithybrid electric vehicle.

[0037]FIG. 4 is a cross-sectional schematic representation of aplanetary gear set.

[0038]FIG. 5 is a simplified schematic view of a one-way clutch shown inFIG. 2.

[0039]FIG. 6 is a schematic depicting control relationships between thevarious systems of a hybrid electric vehicle as coordinated utilizingthe CAN.

[0040]FIG. 7 is a functional schematic depicting the processes, tasksand controls of the various systems of the exemplary hybrid electricvehicle.

[0041]FIG. 8a is a schematic horizontal cross-sectional view of abattery for a hybrid electric vehicle according to one aspect of thepresent invention(s).

[0042]FIG. 8b is a schematic horizontal cross-sectional view of atraditional battery having cylindrically-shaped cells.

[0043]FIG. 8c is a schematic vertical cross-sectional view of a batterycooling system as depicted in FIG. 8a.

[0044]FIGS. 9 and 10 schematically illustrate a method for minimizingdriver perceptible drive train disturbances during take-off in a hybridelectric vehicle.

[0045]FIGS. 11 through 15 schematically illustrate a method forpotentiating the utilizable torque output of a particularly sized enginein a hybrid electric vehicle.

MODE(S) FOR CARRYING OUT THE INVENTION

[0046] As required, detailed embodiments of the present invention aredisclosed herein; however, it is to be understood that the disclosedembodiments are merely exemplary of the invention(s) that may beembodied in various and alternative forms. The figures are notnecessarily to scale; some features may be exaggerated or minimized toshow details of particular components. Therefore, specific structuraland functional details disclosed herein are not to be interpreted aslimiting, but merely as a basis for the claims and as a representativebasis for teaching one skilled in the art to variously employ thepresent invention.

[0047] As depicted in FIGS. 1 and 2, a hybrid electric transportingvehicle 10 has a power train system (having components generallydesignated with reference numbers from the 500's series) includedtherein for providing propulsion, as well as serving supplementalfunctions which are described in greater detail herein. Predominantly,the power train system is positioned in an engine room 11 located near apassenger compartment 12 of the vehicle 10. A battery compartment orhousing 14, also positioned near the passenger compartment 12 holds oneor more batteries 410. As will be appreciated by those skilled in theart, the positioning of both the engine room 11 and battery housing 14is not limited to the locations set forth in FIG. 2. For example, eithermay be positioned in front of, or behind the passenger compartment 12.

[0048] As depicted in FIG. 2, the overall systems architecture of theelectric hybrid vehicle 10 comprises an engine system 510, including aninternal combustion engine 511 (petrol, diesel or the like), that ismechanically connected by an output shaft system 520 to a transaxlesystem 530. The transaxle system 530 is further connected to a driveshaft system 540 utilized to rotate one or more drive wheels 20 thatpropel the hybrid electric transporting vehicle 10. In a preferredembodiment, the combustion engine 511 is controlled by an engine controlmodule (ECM) or unit 220 which is capable of adjusting, among possibleparameters, airflow to, fuel flow to and/or ignition at the engine 511.The engine 511 is mechanically connected via an output shaft 522 to thetransaxle system 530. A planetary gear set 535 establishesinterconnection between the engine 511 (via the output shaft 522), agenerator 532, and the drive shaft system 540 (via the transaxle system530). A motor 531 is also coupled to the drive shaft system 540, alsopossibly via the transaxle system 530.

[0049] In one embodiment, and which is illustrated in at least FIGS. 3and 5, a one way clutch 521 is engageable with the output shaft 522,which in turn is connect to the engine 511 and to the planetary gear set535. The function of the one-way clutch 521 is to limit the engine tobeing only a power/torque input to the planetary gear set 535, and withonly one direction of rotation. Consequently, the one-way clutch 521prevents power or torque from being transmitted from the planetary gearset 535 back to the engine 511.

[0050] In another aspect, and as shown in FIG. 4, the planetary gear set535 comprises a plurality of concentrically positioned planet gears 539mechanically engaged between a perimeter region of a centrally locatedsun gear 538 and an interior surface of a ring gear 537. The individualgears that make up the plurality or set of planet gears 539 are fixed inpositions relative to each other by a planetary carrier 536.

[0051] The generator 532 is mechanically connected to the sun gear 538and is configured to convey rotational power and torque to and from theplanetary gear set 535. In a preferred embodiment, the generator 532 iscapable of being locked to prevent rotation of the sun gear 538 by agenerator brake or lock-up device 533. As further contemplated by thepresent invention, the motor 531 is mechanically connected to the ringgear 537 and is configured to convey rotational power and torque to andfrom the planetary gear set 535. In a preferred embodiment, and asschematically shown in FIG. 3, the drive shaft system 540 is engagablewith the motor 531 and effectively terminates at the drive wheel 20, viawhat can be a conventionally configured transmission/differentialarrangement 542.

[0052] Based on the above disclosed system architecture, implementationof an energy management strategy, which is a focus of the hybridelectric vehicle 10, starts at a high level within a vehicle controlunit or vehicle systems controller (VCU)100 as schematically shown inFIGS. 6 and 7. The vehicle systems controller 100 is programmed withcontrol strategies for the drive train system and battery system, aswell as others. The vehicle systems controller 100 is responsible forinterpreting driver inputs, coordinating the component controllers, anddetermining vehicle system operating states. The VCU 100 also generatescommands to appropriate component sub-systems based on defined vehiclesystems controller 100 functions, and sends those commands to thecomponent controllers that, based thereon, take appropriate actions. Thevehicle systems controller 100 also acts as a reference signal generatorfor the sub-system controllers. The vehicle systems controller 100 maytake the form of a single, integrated microprocessor, or comprisemultiple microprocessors that are suitably interconnected andcoordinated.

[0053] A primary function of the vehicle systems controller 100 is tocarry out vehicle mode processes and tasks (also known as the sequentialcontrol process), as well as make torque determinations, set referencevalues and perform energy management processes. Certain systems of thevehicle 10 are managed or monitored by a vehicle management (VM) unit orcontroller 105 which carries out sequential control processes, includingascertaining the position of the vehicle key and gear selectorpositioning, among others. It is at this level that certain inputs fromthe driver and conditions of the vehicle are synthesized for utilizationas command inputs for sub-system controllers.

[0054] At the lower level of the VCU 100, three sub-componentcontrollers are illustrated in FIG. 7. The first is a high voltage DCcontroller (HVDC) 1 15; the second is a battery management unit orcontroller 110 (bbb); and the third is a drive train controller 120(DTC). As indicated above, certain inputs and processes are taken fromthe driver and the vehicle's systems at the vehicle management unit 105.Conversely, certain outputs relevant to the driver will be transmittedand displayed at the dashboard display unit 107 from the VCU 100 or theVM 105.

[0055] The HVDC 115 is responsible for coordinating operation of thehigh voltage components. The positioning of this controller isschematically shown in FIG. 6. The HVDC contains contactors or breakerswhich are normally positioned to an open configuration that preventselectricity from flowing thereacross. But when called on to take actionand engage the battery 410, for instance when starting of the engine 511is required, these contractors (usually a pair) close completing anappropriate connective circuit.

[0056] As shown in FIG. 6, the HVDC serves as a shield or buffer betweenthe high voltage battery 410, and the inverters 534, as well as otherauxiliary loads run off of the electric power of the battery 410. Anexample of such a high voltage auxiliary load may include anelectrically run air-conditioning compressor system. In order to act assuch a buffer, the high voltage output from the battery 410 must berelatively slowly “brought-up” to operating levels at the inverter 534and/or auxiliary loads. In order to accept this “run-up” of the voltage,relatively small capacity contactors are initially closed that causevoltage from the battery to pass to a capacitor in either the inverter534 or the appropriate auxiliary load, across a resistive circuit (acircuit containing buffering resistors). Once an appropriate pre-chargeis built-up in the capacitor, primary contractors are then closed whichcomplete the high voltage circuit between the batteries 410 and thecapacitor contained within the receiving component which may beexemplified by the DC to AC inverter(s) 534, or an auxiliary load suchas an electric air-conditioning system as indicated hereinabove. In thismanner, a potentially damaging high voltage is prevented from beingintroduced too quickly to the receiving components.

[0057] The HVDC 115 also carries out certain diagnostic functionsregarding the components of the HVDC 115, such as the contactors withinthe HVDC 115 itself, and also possibly the several systemsinterconnected through the HVDC, such as the battery 410, the inverters534, or an electrically driven air-conditioning compressor which has notbeen illustrated in the Figures. Among other parameters, thesediagnostics may be performed based on measurements of voltage and/orcurrent.

[0058] The HVDC 115 also provides interconnection between an exteriorcharger connection (see ext. charger in FIG. 6), thereby allowing thebattery 410 to be “plugged-in” for charging from an external powersource.

[0059] The battery management controller (BMU) 110 handles control tasksrelative to the battery system 410. Among other characteristics, the BMU110 can estimate and measure state-of-charge (SOC) levels, and voltageand current parameters. It can also sense/determine and maintain maximumand minimum voltage and current levels with respect to the battery 410.Based on these determinations or sensed quantities/qualities, the VM105, via such control modules as the DTC 120, can direct certainoperations for affecting changes in the SOC of the battery 410. Othercharacteristics which may be monitored include operating temperature(s)of the battery 410, and voltages at the individual battery cells 412.Similarly, pressure within the cells 412 can also be monitored. Failuresmay be detected and reported, at least back to the VCU; but there isalso the possibility of the information being passed to the operator viathe dashboard display unit 107.

[0060] The DTC 120 makes the mode selection under which the severalpowering components will cooperate. That includes choices betweenparallel and split modes, as well as positive and negative split modes.The operational points for the several components of the drive train arealso specified by the DTC 120. Still further, reference values areprovided by the DTC 120 for the several sub-systems, including thetransaxle management control modules or unit (TMU) 230 and the enginecontrol module or unit (ECM) 220. From among the possible settingsestablished by the DTC 120, battery charging/discharging mode is apossibility, as well as specifying whether the generator 532 and/ormotor 531 should be used in their powering capacity as a motor, or theirgenerating capacity as a generator. Torque references for the generatorand motor are also issued from the TMU 230.

[0061] As a sub-component under the TMU 230, the transaxle control unitTCU 232 handles the transaxle 530 with respect to torque compensationwhen starting and stopping the engine 511. The TCU 232 uses and controlstwo slave processors characterized as a generator control unit GCU 236and a motor control unit MCU 234. The GCU 236 handles the current andtorque control of the generator 532; typically, via the inverter 534.The GCU 236 receives its torque and speed reference information from theTCU 232 as its immediate controller. The TCU 232 receives a total torquereference for the transaxle 530 and the speed reference value for theengine 511, together with mode reference information regardingcooperation between the engine 511 and generator 532; such as, whetherparallel-, positive-split, or negative-split mode configurations will beassumed. The TCU 232 generates the torque reference parameters for thegenerator 532 and motor 531, each of which are implemented under thecontrol of the GCU 236 and MCU 234, respectively. The specified torquesettings are accomplished by controlling the current provided to therespective generator/motor controllers 236, 234.

[0062] Based on a map of optimal engine torque vs. speed curves, enginespeed and torque are selected by the DTC 120 so that the engine system510 can deliver the desired engine power and simultaneously lie on oneof the engine's optimized efficient curves. If the DTC 120 determinesthat the speed of the engine 511 is too low for efficient operation,then the engine 511 is turned (or left) off by the engine control unit220. If the power train control module 120 determines that the speed ofthe engine 511 is too high to be controlled by the generator 532 (basedon SOC and generator limitations), the engine 511 is set to a slowedoperational speed by the ECM 220.

[0063] Once the speed, torque and power of the engine 511 are determinedby the vehicle systems controller 100, particularly at the DTC120 of thecontroller 100, then the DTC 120 further determines the required speedand torque of the generator 532 to control the engine 511. The DTC 120,using this information, then determines the required speed and torque ofthe motor 531 to meet the difference, if any, between driver power(torque) demand and the engine power (torque).

[0064] Torque determination and monitoring is also carried out at theVCU 100. This function further ensures that torque delivered to thedrive wheel(s) 20 is substantially equal to the torque (acceleration)demanded by the driver. The VCU 100 also monitors and controls thetorque from the engine 511 and transaxle system 530 by comparing asensed torque against the torque demanded by the driver. Torquemanagement by the VCU 100 interprets driver inputs and speed controldemands to determine regenerative brake torque and desired output shafttorque.

[0065] From the VCU 100, commands and references are distributed over acontroller area network (CAN) 300 to component controllers generallyreferenced herein utilizing reference numbers in the 200's series. Asindicated above, these controllers include the ECM 220 and the TMU 230that together control the power train system to achieve efficient energymanagement, partition torque, determine engine 511 operating point(s),and decide on, and coordinate engine 511 start/stops. Commands andreferences from the VCU 100 to a series regenerative brake controllerdetermine regeneration torque limitations, desired regenerative torqueand zero vehicle speed control.

[0066] Finally, if and/or when individual system components are renderedinoperative, such as the motor 531 becomes disabled, the VCU 100 isconfigured to provide limited operating control over the power trainsystem to allow the hybrid engine vehicle 10 to “limp” home.

[0067] As shown in FIG. 8a, a compact battery system 400 is made up of anumber of elongate battery cells 412, each cell 412 having alongitudinal axis and a hexagonal cross-section shape in a planeoriented substantially perpendicular to the longitudinal axis. Each cell412 is parallelly oriented to each other within a battery housing 14. Asshown in FIG. 8a, the plurality of cells 412 are arranged in a honeycombconfiguration with opposed faces of adjacent cells 412 proximatelylocated one to the other in face-to-face relationship. One or morehexagonally shaped cooling channels 442 are located at an interiorlocation(s) amongst the plurality of battery cells 412. As appreciatedby those skilled in the art, a significant amount of volume is unusedand wasted in battery compartments configured to hold traditionalcylindrical battery cells as is exemplarily depicted in FIG. 8b.Furthermore, the traditional cooling system often requires the use of asystem of fluid filled pipes to cool a fraction of the cylindricallyshaped battery cells' curved exterior surface. In contrast, the batterycooling system 440 for the hexagonal battery cells 412, as depicted inFIG. 8a, presents a greater surface area for heat exchange to takeplace.

[0068] In another aspect of the system 440, and as is shown in FIG. 8c,a thermally radiative cap 443 is in fluid communication with one or moreof the cooling channels 442 which is filled with a cooling fluid 445that circulates between the cap 443 and the channels 442 to cool thebattery cells 412. The cooling fluid 445 may consist of water maintainedunder a vacuum so that it boils at approximately 40° centigrade.Circulation of the fluid, as well as transformation between the gaseousand liquid states, occurs because of the temperature differentialbetween the warmer lower area among the battery cells 412 and the coolerupper area with the cap 443. Exemplarily, this temperature ofvaporization or boiling advantageously falls between these warmer andcooler temperatures.

[0069] An air circulation system cools the battery arrangement bydrawing air through an air inlet exposed to the passenger compartment 12and directs the air along a circulation path that crosses the radiativecap 443. The temperature of the air drawn from the passenger compartment12 is normally in a range suited for passenger comfort, a temperaturenormally well below 40° centigrade. The intake may also pull air fromoutside the vehicle if ambient conditions are favorable. Air sourceselection may be easily accomplished using a flap-style valve common inother air duct environments.

[0070] After traversing the circulation path, the cooling air is mostpreferably discharged away from the passenger compartment 12 to avoidcirculation and the introduction of heat and potentially airbornecontaminants into the passenger compartment 12 that may have been pickedup from the battery system 400. The risk of this occurrence, however, isreduced significantly through this battery's 410 configuration in whichthe circulated air passes over the closed system of the battery and itshousing, and not through or near the more hazardous chemical cells 412.

[0071] To further promote cooling, the radiative cap 443 may beconfigured with a plurality of fin-type members 444 that extend from anexteriorly exposed surface thereof for enhancing thermal discharge ofheat from the cap 443 to air circulated across the fins 444.

[0072] In another aspect, the disclosed invention(s) include a methodfor potentiating an engine's 511 power contribution to a hybrid electricvehicle's 10 performance in a take-off operating condition. Normally,fuel injection to, and ignition at the engine 511 are only commencedwhen the engine 511 is operating at a speed exceeding the resonancespeed of the drive train to reduce engine start harshness; suchresonance speeds of the drive train being dictated, at least in part, bytransmission backlash, softness and the like. During high driveracceleration demands, however, ignition and the injection of fuel isdesirably started as early as possible to potentiate output power andacceleration. The present method amends this typical operation andincludes initiating take-off acceleration of the vehicle 10 exclusivelyusing the motor 531, predicting the future demand for an engine's 511power contribution to the vehicle's 10 immediate future power demandduring the take-off acceleration, and starting the engine 511 at thetime that the determination is made of future demand for the engine's511 power contribution during the take-off acceleration. This fulltake-off control method or process further includes making theprediction of future demand at the initiation of take-off accelerationand/or increasing the speed of engine 511 operation as rapidly aspredetermined operating efficiency parameters permit. The full take-offcontrol method which increases the speed of engine 511 operation asrapidly as predetermined operating efficiency parameters permit may alsoinclude a step of allowing the increase in speed of engine operation toprogress to a predetermined peak efficiency rate and diverting excesspower from the engine 511 to the generator 532 that generateselectricity with the diverted power. This full take-off control methodwhich increases the speed of the engine 511 operation as rapidly aspredetermined operating efficiency parameters permit, may also include astep of allowing the increase in speed of engine 511 operation toprogress to a predetermined peak efficiency rate which enables exclusiveutilization of the engine 511 to meet the entirety of the vehicle's 10future power demand and reducing the motor's 531 contribution to thepower supplied to the vehicle 10 so that no excess power above demand issupplied by the engine 511.

[0073] In still a further aspect, the present invention provides aprocess or method for maintaining a catalyst 702 of an emissions system700 in a hybrid electric propulsive system in an operative state. Themethod calls for sensing that the engine 511 has stopped operating. Atime period is then predicted after which the catalyst 702 will cooldown below a temperature (also known as a light-off temperature) atwhich the catalyst becomes ineffective. Pursuant thereto, the engine 511is restarted when the time period has expired or lapsed, therebymaintaining the catalyst 702 at temperatures in excess of the light-offtemperature, regardless of whether power is need from the engine 511 atthat time. Predicting the time period after which the catalyst 702 willcool down takes into consideration known qualities of the catalyst 702and ambient conditions in which the hybrid electric vehicle 10 is beingoperated. Such known qualities of the catalyst 702 include, but are notlimited to, heating and cooling characteristics of the catalyst 702,life expectancy of the catalyst 702, and age of the catalyst 702.Relevant ambient conditions in which the vehicle 10 is being operatedinclude, but are not limited to, weather and environmental conditionssuch as temperature, humidity and contaminant loads, as well as trafficconditions and road conditions. As an example, if driving is occurringin hilly terrain, this can be sensed as a cyclical demand for enginepower for recurring uphill climbs. If this is quantified, it may beconsidered in the control parameter as a predictable occurrence.Additionally, the system may take into account sensed or “learned”driver habits or performance for predicting purposes which can includethe a particular driver's demand for power is cyclical or otherwisepatterned. This may be typified by some drivers' bad habit of repeatedlyaccelerating to a speed, and then subsequently slowing therefrom. Whenthe decrease in speed is realized by the driver, rapid acceleration isthen demanded for again setting the desired travel speed. If the controlsystem “learns” such a pattern, it may be utilized in the predicting orcalculating process for maximum elapse time before the catalystexcessively cools.

[0074] This method for maintaining the exhaust catalyst 702 in anoperative condition may also include sensing the catalyst's 702temperature and initiating operation or stopping of the engine 511 whena predetermined temperature is detected. Because of the hybrid's 10characteristics, the catalyst maintenance process may further includerunning the engine 511 at idle speed when temperature elevation isrequired and charging the batteries 410 with the power produced from theidling engine 511. An alternative aspect to this process calls forheating the catalyst 702 to a predetermined temperature differentialabove the light-off temperature and then stopping operation of theengine 511 when the predetermined temperature differential is achieved.Engine operation is stopped when the predetermined temperaturedifferential is detected by a temperature sensor 704 monitoring thetemperature of the catalyst 702 or is predicted by a catalysttemperature model.

[0075] A method for minimizing driver perceptible drive traindisturbances during take-off driving in a hybrid electric vehicle 10when maximized power is often desired is also described herein. Theconcepts of this method are illustrated in FIGS. 9 and 10. The methodincludes sensing an actual state-of-charge (SOC) value of the battery410 in a hybrid electric vehicle 10 and a traveling velocity of thevehicle 10 during take-off operation. The sensed actual SOC value iscompared with a SOC reference value and a delta SOC value is computed asa difference therebetween. A velocity-based SOC calibration factorcorresponding to the traveling velocity of the vehicle 10 is obtainedfrom a look-up table maintained in the control system. A combination ofthe delta SOC value and the SOC calibration factor are utilized as a SOCfeedback engine speed control instruction to the engine control unit(ECM) 220 of the hybrid electric vehicle 10. A driver's desiredvehicular acceleration based on accelerator position is also sensed. Amaximum possible engine power generatable at the sensed vehicle speed isdetermined, as is a required power value from the power train of thevehicle to meet the driver's desired vehicular acceleration. The maximumpossible engine power generatable at the sensed vehicle speed iscompared with the required power value and a delta power trainrequirement value is computed as a difference therebetween. Avelocity-based and accelerator position-based power calibration factorcorresponding to the traveling velocity of the vehicle and theaccelerator position is determined from a second look-up table. Acombination of the delta power train requirement value and the powercalibration factor is utilized as a power requirement feed-forwardengine speed control instruction to the engine controller 220 of thehybrid electric vehicle 10.

[0076] The combination of the delta SOC value and the SOC calibrationfactor is by multiplication, as is the combination of the delta powertrain requirement value and the power calibration factor is bymultiplication.

[0077] In a separate or enhancing aspect of the method outlinedimmediately above, a take-off vehicle operating condition is detected inwhich maximized power is likely to be demanded from the drive train ofthe hybrid electric vehicle 10. A sensed SOC discharge condition duringthe take-off operation due to motor utilization of battery power isprevented from triggering a battery charging condition which wouldreduce engine torque available to power the drive train of the vehicle10. Alternatively, and/or additionally, immediate acceleration of theengine's 511 operation beyond an optimized operational speed inanticipation of an actual maximized power demand is initiated. Stillfurther, a command may be issued from a generator controller (GCU) 236,responsive to a sensed SOC discharge condition, instructing immediateacceleration of the engine's 511 operation beyond an optimizedoperational speed thereby minimizing discharge of the battery 410 orcommencing recharge of the battery 410.

[0078] A preferred SOC reference value, of exemplarily , but notnecessarily, fifty percent of battery 410 total charge capacity, isutilized in at least one embodiment of the invention; on others, a morelenient range of forty to sixty percent of battery total charge capacitymay be observed.

[0079] In another aspect, the invention takes the form of a method foroptimizing the operational efficiency of a hybrid electric vehicle 10.The method includes operating an engine 511 of a hybrid electric vehicle10 preferentially on an optimized power curve of the engine 511 formaximizing the efficiency of the engine 511. A state-of-charge (SOC)condition of a battery 410 of the hybrid electric vehicle 10 is sensedand constitutes a preferential value indicative of no additionalcharging being desired. At cruising, however, the engine power output inparallel mode is too large along the engine's 511 optimized power curve,particularly in view of gear ratios set by acceleration requirements.Instead of using negative-split mode and suffering the inherent lossesof that configuration, the running torque of the engine 511 in parallelmode is reduced to a level below the optimized torque curve to a pointthat the power produced by the engine 511 is substantially equal to thepower demanded for driving the hybrid electric vehicle 10.

[0080] The reduction in engine torque is affected by adjusting airflowto, fuel flow to and/or ignition parameters of the engine 511.

[0081] The drive train of the hybrid electric vehicle 10 is thusreconfigured from a negative power-split mode in which engine power issplit through a planetary gear arrangement 535 between the drive wheels20 and the generator 532 to a parallel mode in which the generator 532is locked and all engine power is output to the drive wheels 20 of thehybrid electric vehicle 10 through the planetary gear arrangement 535.This parallel mode, but with reduced and non-optimized engine operation,is used when efficiency is higher in this mode than if using negativesplit mode for the same torque output.

[0082] As a goal, the time spent in negative power-split mode isminimized and time spent in parallel mode is maximized. Utilization ofthe generator to motor the engine 511 to a slowed operational speed isavoided using this process thereby avoiding sequential charge anddischarge cycles through the drive train components of the hybridvehicle. Energy losses in the power train of the hybrid electric vehicle10 are therefore reduced by avoiding charge and discharge of the hybridelectric vehicle's battery system 400. Cooling requirements for thehybrid electric vehicle's battery 410 are also reduced since batterylosses are decreased.

[0083] In yet another aspect, the present invention takes the form of amethod for calibrating and synchronizing sensed operating torques of theengine 511 and the generator 532 in a planetary gear based hybridelectric vehicle 10. The method includes providing a sensor that detectsthe operational torque of the engine 511 at the engine's interface withthe planetary gear system 535 (power-split hybrid drive train) of thehybrid electric vehicle 10. A sensor is provided that detects theoperational torque of the generator 532 at its interface with theplanetary gear system 535 of the hybrid electric vehicle 10. Theplanetary gear system 535 of the hybrid electric vehicle 10 is operatedin the split mode so that the generator 532 is directly linked to theengine 511 and a reading of the sensor that detects the operationaltorque of the generator 532 may also be used to compute the operatingtorque of the engine 511. Paired values of sensed operational speeds ofthe engine 511 and the generator 532 at like times are recorded. Eachpair of recorded values is arithmetically processed and a calibratingvalue therebetween is computed. The sensing and recording of pairedvalues at the same sensed generator and engine operation points isrepeated thereby enabling the calculation of computed averagecalibrating values at each of the particular sensed generator and enginespeeds and torques suitable for subsequent utilization in computingcorrelating engine torques in the future. The engine 511 and thegenerator 532 are controlled utilizing the average calibrating value atfuture times of transition between power-split mode and parallel mode ofthe planetary gear system 535 so that the engine torque is substantiallymatched with the generator torque at the time of direct linkage acrossthe planetary gear arrangement (i.e., when releasing generator lock-up),thereby avoiding driver detectible irregularities or harshness in theperformance of the power train of the hybrid electric vehicle 10.

[0084] The predictability of the relationship between the engine 511 andgenerator 532 in the parallel mode is based on gear ratios that remainsubstantially unchanging.

[0085] Contemporaneously measured values of complementary operatingparameters of the hybrid electric vehicle 10 may also be recorded foreach pair of recorded values of sensed operational torques of the engine511 and the generator 532 to be used supplementally in the torquematching process.

[0086] To maintain trueness, the average calibration value is permittedto be varied by a limited maximum value with respect to time so thatanomalous disturbances do not significantly impact the computed averagecalibration value. The updating of the computed average calibrationvalue for a particular generator sensed speed is ongoing, and continuousthereby continually improving the quality of the average calibrationvalue for that particular generator sensed speed.

[0087] The irregularities to be avoided are manifest as jerking motionsinduced in the hybrid electric vehicle 10 by the planetary gear system535. Customization of the computed average calibration value to anindividual vehicle is enabled via the invention in the presentlydisclosed embodiment since histories are taken, maintained, andconsidered in the matching process.

[0088] Referring to FIGS. 11-15, yet another aspect of the presentinvention is disclosed. This aspect takes the form of a method forpotentiating the utilizable torque output capacity of a hybrid electricvehicle 10. The method includes controlling operation of the engine 511of the hybrid electric vehicle 10 using the generator 532, the engine511 and generator 532 being interconnected through the planetary gearsystem 535. The generator 532 has approximately equal torque outputcapacity as the engine 511 when connecting gear ratios are considered.An engine controller 220 is utilized for managing the engine's 511operation thereby permitting the engine 511 to be operated at a torqueoutput level substantially equal to the maximum torque output of thegenerator 532 without a significant margin of excess control capacity ofthe generator 532 over the engine 511. An overpower condition isdetected in which the torque output of the engine 511 is surpassing themaximum torque output of the generator 532. Responsively, the engine 511is controlled to a torque output that is less than the maximum torqueoutput of the generator 532.

[0089] The method continues by rechecking for a continuation of theengine overpower condition and shutting the engine 511 down if thecontrol actions are not sufficient and a continuing overpower conditionis detected. In this manner, generator and engine over-speed is avoided.

[0090] By this process, total utilizable capacity of the hybrid electricvehicle's power plant is optimized by enabling running the engine 511 atsubstantially maximum capacity where greatest torque is producedtherefrom.

[0091] Available take-off torque in the hybrid electric vehicle 10 isoptimized by running the engine 511 at substantially maximum torquecapacity together with a commensurately sized, but not oversized,generator 532 with respect to relative torque capacities. Torque outputof the engine 511 and the generator 532 are calculated based on detectedoperational speeds of the engine 511 and the generator 532,respectively. Speed error may be calculated utilizing one or twosensors.

[0092] In a supplemental embodiment of this general control concept, acommand is issued to increase the torque output of the generator 532responsively to detection of an engine 511 over power condition. A checkfor the continuation of the engine overpower condition is repeated. Thenagain, a continuing overpower condition may be detected in which thetorque output of the engine 511 continues to surpass the torque outputof the generator 532 and a supplemental command is issued to againincrease the torque output of the generator 532. Again, the check for acontinuation of the engine overpower condition is repeated. Ultimately,the engine torque is reduced back to a torque output that is less thanthe torque output of the generator 532 when repeated checks, of apredetermined number, each detects an overpower condition in which thetorque output of the engine 511 surpasses the torque output of thegenerator 532.

[0093] In yet another embodiment of this same basic concept, the methodincludes detecting an overpower condition in which the torque output ofthe engine 511 is surpassing the maximum torque output of the generator532; the engine 511 is responsively controlled to a maximum torqueoutput set at a value less than the maximum torque output of thegenerator 532.

[0094] Referring now with greater specificity to the drawings, FIGS. 11and 12 comparatively illustrate the presentmethod of control whichenables the elimination of a thirty percent (30%) “buffer” that has beenconventionally provided between the torque capacities of the engine 511and the generator 532; the necessity of this buffer resulting in the useof generators 532 significantly larger, or engines 511 significantlysmaller than would otherwise be optimal since thirty percent of one oftheir capacities must be sacrificed to maintain the buffer margin forcontrol, just in case it is needed. By otherwise controlling the engine511 so that it can be assured that the capacity of the torque capacityof the generator 532 will not be exceeded, the approximately thirtypercent of lost capacity can be exploited. Graphically this is shown inFIG. 12 where the speed (ω), plotted on the x-axis, is equalized at theright side of the graph where the maximum torque of the generator(T_(gen) _(—) _(max)) is equal to the torque of the engine 511 when theconstant (K) representing the gearing ratio is considered (T_(eng)/K)The increase in useable speed, and in turn useable power (P=T·ω), fromboth the engine 511 and generator 532 is represented by the distancemoved to the right along the x-axis from the buffered position(K·Δω_(eng) _(—) _(max)) to the “virtualized” position (K·Δω_(eng) _(—)_(max) _(—) _(virt)) where the buffer is virtual, and not actual,because of the control strategy exercised.

[0095] Referring now to FIGS. 13-15, the VCU 100 calculates an enginereference value (ω_(eng) _(—) _(ref)) and the TMU 230 receives thatvalue and, together with a sensed speed of the motor (ω_(motor)), takinginto account the gearing ratio consequence, a generator reference speed(ω_(gen) _(—) _(ref)) is calculated and passed forward for comparison,by summation, with the actual generator speed (ω_(gen)). The result ofthat comparison is then processed through a proportional integralcontroller (PI) for, among other things, amplifying the error value and“learning” error patterns that continue over periods of time based onhistorical values. The learning process is enabled by performingrepetitive calculations. From the PI controller, a generator torquereference (T_(gen) _(—) _(ref)) is derived. This reference is passed tothe generator torque controller 236 for operational control purposes;i.e., by adjusting current, by adjusting voltage with is accomplishedusing pulse width modulation using transistors in the inverter (see FIG.6). The same reference (T_(gen) _(—) _(ref)) is further processed bysubtracting therefrom the maximum torque capacity of the generator(T_(gen) _(—) _(max)(ω_(gen))). The sense, whether positive or negative,of this outcome is then determined; if negative, the maximum torquecapacity of the generator has not been exceeded; if positive, themaximum torque capacity of the generator has been exceeded. If positive,the capacity of the generator is being exceeded. This positive value isthen multiplied by the constant K to take into account the effect of thegearing ratio and thereby calculating a modification torque(T_(modification)).

[0096] To the ECM 220, an engine torque reference (T_(eng) _(—) _(ref))is supplied from the VCM 100. At the ECM 220, the engine torquereference (T_(eng) _(—) _(ref)) is compared to the maximum torque of theengine (T_(eng) _(—) _(max)) The smaller (min) of these two values isfurther processed by comparison with the modification torque(T_(modification)) which is subtracted therefrom producing a modifiedengine torque reference (T_(eng) _(—) _(ref) _(—) _(mod)). Thisreference (T_(eng) _(—) _(ref) _(—) _(mod)) is fed forward to the enginetorque controller 220 for operational control purposes over the engine511; i.e., for adjusting, among possible parameters, airflow to, fuelflow to and/or ignition at the engine 511. In practice, if the generator532 has not been determined to be in a condition overpowering the engine511 at the TMU 230, then the engine torque reference (T_(eng) _(—)_(ref)) from the VCU 100 will be processed through to the engine 511.If, however, there is a torque modification value (T_(modification))from the TMU 230 that is not zero, the engine 511 will be controlled toeliminate the condition in which the engine torque exceeds that of thegenerator 532.

[0097] A primary benefit of the above described arrangement is that asingle controller, the TMU 230, provides both the (ω_(gen) _(—) _(ref))and the (ω_(gen)). This avoids the possibility of introducing errorsthat are attributable to mis-calibrations that can otherwise occur whenmultiple controllers are employed for similar purposes. Still further, amaximum engine torque limit (T_(eng) _(—) _(max) _(—) _(lim)) may bederived at the TMU 230 to provide dc over-voltage protection, but whichis affected at the engine torque control unit 220.

[0098] In the embodiment illustrated in FIG. 14, two Pl controllers areincorporated. In the embodiment of FIG. 15, the modified engine torquereference (T_(eng) _(—) _(ref) _(—) _(mod)) and the maximum enginetorque limit (T_(eng) _(—) _(max) _(—) _(lim)) are rationalized toproduce the maximum engine torque limit (T_(eng) _(—) _(max) _(—)_(lim)) that will be utilized by the engine torque controller 220.

[0099] Although the present invention has been described and illustratedin detail, it is to be clearly understood that the same is by way ofillustration and example only, and is not to be taken as a limitation.The spirit and scope of the present invention are to be limited only bythe terms of any claims presented hereafter.

What is claimed and desired to be secured by Letters Patent is asfollows:
 1. A method for potentiating the utilizable torque outputcapacity of a hybrid electric vehicle, said method comprising:controlling operation of an engine of a hybrid electric vehicle using agenerator, the engine and generator being interconnected through aplanetary gear system, the generator having approximately equal torqueoutput capacity as the engine based on connective gear ratio selection;and utilizing an engine controller for managing the engine's operationthereby permitting the engine to be operated at a torque output levelsubstantially equal to the maximum torque output of the generatorwithout a significant margin of excess control capacity of the generatorover the engine; detecting an overpower condition in which the torqueoutput of the engine is surpassing the maximum torque output of thegenerator; and controlling the engine to a torque output that is lessthan the maximum torque output of the generator.
 2. The method asrecited in claim 1 further comprising: rechecking for a continuation ofthe engine overpower condition; and shutting the engine down when acontinuing overpower condition is detected.
 3. The method as recited inclaim 1 further comprising: rechecking for a continuation of the engineoverpower condition; and shutting the engine down if an engine overspeed is detected.
 4. The method as recited in claim 1 furthercomprising: rechecking for a continuation of the engine overpowercondition; and shutting the engine down if a generator over speed isdetected.
 5. The method as recited in claim 1 further comprising:optimizing total utilizable capacity of the hybrid electric vehicle byenabling running the engine at substantially maximum capacity wheregreatest proportional torque is produced by the engine.
 6. The method asrecited in claim 1 further comprising: optimizing available take-offtorque in a hybrid electric vehicle by running the engine atsubstantially maximum torque capacity together with a commensuratelysized generator with respect to torque capacity.
 7. The method asrecited in claim 1 further comprising: calculating torque output of theengine and the generator based on detected operational speeds of theengine and the generator, respectively.
 8. The method as recited inclaim 7 further comprising: calculating speed error utilizing a singlesensor.
 9. The method as recited in claim 7 further comprising:calculating speed error utilizing two sensors.
 10. A method forpotentiating the utilizable torque output capacity of a hybrid electricvehicle, said method comprising: controlling operation an engine of ahybrid electric vehicle using a generator, the engine and generatorbeing interconnected through a planetary gear system, the generatorhaving approximately equal torque output capacity as the engine; andutilizing an engine controller for managing the engine's operationthereby permitting the engine to be operated at a torque output levelsubstantially equal to the maximum torque output of the generatorwithout a significant margin of excess control capacity of the generatorover the engine; detecting an overpower condition in which the torqueoutput of the engine surpasses the torque output of the generator;issuing a command to increase the torque output of the generator;repeating the check for a continuation of the engine overpowercondition; and reducing engine torque back to a torque output that isless than the torque output of the generator when repeated checks of apredetermined number each detects an overpower condition in which thetorque output of the engine surpasses the torque output of thegenerator.
 11. The method as recited in claim 10 further comprising:repeating the check for a continuation of the engine overpower conditionafter the first issued command to increase the torque output of thegenerator; detecting a continuing overpower condition in which thetorque output of the engine continues to surpass the torque output ofthe generator; issuing a supplemental command to again increase thetorque output of the generator.
 12. A method for potentiating theutilizable torque output capacity of a hybrid electric vehicle, saidmethod comprising: controlling operation an engine of a hybrid electricvehicle using a generator, the engine and generator being interconnectedthrough a planetary gear system, the generator having approximatelyequal torque output capacity as the engine; and utilizing an enginecontroller for managing the engine's operation thereby permitting theengine to be operated at a torque output level substantially equal tothe maximum torque output of the generator without a significant marginof excess control capacity of the generator over the engine; detectingan overpower condition in which the torque output of the engine issurpassing the maximum torque output of the generator; and controllingthe engine to a maximum torque output set at a value less than themaximum torque output of the generator.